This invention relates to treatment of crude soapstock byproduct from alkali refining of triglyceride oils and more particularly to an improvement in process for recovering free fatty acid from the crude soapstock.
Alkali refining of triglyceride oils comprehends treatment of the oils with strong (typically 10.degree.-20.degree. Baume') caustic soda to remove a variety of impurities therefrom such as free fatty acid, phosphitides, unsaponifiable material, and the like. Usually excess caustic solution (to neutralize all the free fatty acid present) is mixed with the oil at about 20.degree.-35.degree. C. This causes an emulsion to form. Such emulsion then is heated at about 55.degree.-65.degree. C. for breaking it, and the resulting alkali refined oil is recovered by conventional techniques such as by filtering, decanting, centrifuging, or the like. The major byproduct formed by breaking the emulsion is alkali metal soap of the free fatty acid (crude soapstock) having oil entrained therein and typically contaminated with minor amounts of gums, slimes, and phosphatides. Various washwater streams for cleaning equipment and the like also can contain crude soapstock as well as water used in processing fatty emulsifiers (eg., monoglycerides), stearines, and the like. These other soapstock-containing water streams also can be processed by the present invention for recovery of their free fatty acid content.
Usually crude soapstock from edible oil refineries is sold to the animal industry for feed or it can be acidulated with mineral acid (typically sulfuric acid of 98% strength) to form a fatty acid stream from which 40-45% of the free fatty acid initially in the soapstock can be recovered. The crude soapstock appears as a viscous mass which typically can be made flowable only by dilution with water and heating.
Heretofore it has been proposed (Canadian Pat. No. 979,889) to saponify the crude soapstock followed by subjecting the saponified soapstock to solvent extraction to remove a variety of contaminant materials. The extracted mixture then is acidulated to spring the free acid which is separated by conventional separation techniques.
Advantages of the present invention include recovery of greater than 90% of the free fatty acid content from the crude soapstock fed to the process, reducing viscosity of the soapstock, and obtaining a clean separation of free fatty acid from acid water in a separation step of the process. Additionally, byproduct inorganic salt (preferably sodium sulfate) dissolved in water is withdrawn from the process, which inorganic salt solution has commercial value.